It is well known that refrigeration systems have means for handling a refrigerant in such a way that heat is rejected from the system at a relatively high temperature and absorbed at a relatively low temperature. Provision can be made for making use of either or both of these conditions. Use of the heat rejecting portion of the system ordinarily leads to characterizing the system as a heat pump. The use of heat pumps has increased in recent years due to their efficiency in producing heat as compared with various other means.
The interconnection of two or more closed loop refrigeration systems in which the heat absorbing stage of one is in heat exchange relation with the heat rejecting stage of the other, is also well known in the art and is commonly termed a cascade system. One of the primary purposes of a cascade system is to permit the attaining of temperatures in the heat rejecting or heat absorbing stage of one of the systems that exceeds that which can be attained if only a single system is used with commonly available heat rejecting or heat absorbing loads. An example of a cascade coupled heat pump system for heating water is disclosed in the U.S. Pat. to Gustafsson No. 3,984,050. In it, water is heated by passing in heat exchange relationship with the condenser of one of the heat pump systems.
A heat pump water heater is also disclosed in the U.S. Pat. to Ruff No. 2,516,094. Other heaters using refrigeration systems are disclosed in the U.S. Pat. to Bahel et al Nos. 4,194,368, McGrath 2,242,588 and Buchanan 2,102,940.